Hi there Nernico. You are right in saying that energy cannot be created or destroyed however thanks to entropy the universe is heading towards its maximum state of disorder. This essentially means eventually the energy will be spread out evenly, it is currently thought that this will lead to heat death in about 10100 years.

There are other ideas regarding the http://en.wikipedia.org/wiki/Fate_of_the_universe" [Broken] (creating a new universe) but as I understand it the heat death is the only idea that has evidence to support it.

In the end, all matter energy will eventually become radiation energy. And radiation energy tends to dilute as the fourth power of the scale factor, so that in an expanding universe, the total energy in a set comoving volume decreases with time (a comoving volume is one that expands along with the expansion of the universe). In these coordinates, the total energy of a comoving volume of the universe tends towards zero.

The article doesn't support what you said in #3, that "all matter and energy eventually leaves the universe the same way as it entered, through a singularity or singularities (as in black holes)." It talks about converting baryonic matter into photons through hawking radiation.

In the end, all matter energy will eventually become radiation energy.

I don't think this is quite right. There is no reason to believe that every single atom in the universe will get consumed by a black hole and then recycled into Hawking radiation. This is actually one of the problems with Penrose's CCC. To make CCC work, he needs 100% conversion of baryonic matter into photons, but theory doesn't offer any reason to believe that it will be 100%.

I don't think this is quite right. There is no reason to believe that every single atom in the universe will get consumed by a black hole and then recycled into Hawking radiation. This is actually one of the problems with Penrose's CCC. To make CCC work, he needs 100% conversion of baryonic matter into photons, but theory doesn't offer any reason to believe that it will be 100%.

Would an individual atom not eventually decay into something else or are they perpetually stable? I'm not proposing that it will decay I genuinely don't know.

Even if proton decay exists, there are other forms of matter such as neutrinos that are stable as far as we know, and in the far future you can also have individual electrons that end up isolated inside their own cosmological event horizons forever.

This is actually one of the problems with Penrose's CCC. To make CCC work, he needs 100% conversion of baryonic matter into photons, but theory doesn't offer any reason to believe that it will be 100%.

Ben, all matter ending up in black holes is one of the possibilities discussed here and it stuck with me for decades. Perhaps it is no longer considered likely. Dark energy expansion of the universe may help prevent it.

"Chunks of matter and binary black dwarfs will merge together creating new black holes, and these black holes will be consumed by even larger black holes. It might be that in the far future, all matter will exist in a few, truly massive black holes."

Talking with the high energy physics people, proton decay is generally expected to be inevitable. That is why all matter will eventually become radiation.

Sorry, but I'm not buying it based on your secondhand impression that other people think it's inevitable. In any case, it has nothing to do with the arguments about neutrinos, or electrons isolated inside cosmological horizons. There's also the issue of dark matter, which is probably stable as well, although we know almost nothing about it.

I wasn't pointing you to the paper to say that I think CCC is right. I was pointing you to the paper because it discusses the reasons why it is incorrect to claim that all matter will become radiation. Penrose would like all matter to become radiation, because it's necessary if he wants CCC to work. Nevertheless he honestly surveys what we know about the question, and concludes that based on current knowledge of particle physics, it won't happen. For this reason, one of the predictions he was originally pushing as part of CCC was nonstandard particle physics that would allow what you're claiming to be true.

Ben, all matter ending up in black holes is one of the possibilities discussed here and it stuck with me for decades. Perhaps it is no longer considered likely. Dark energy expansion of the universe may help prevent it.

"Chunks of matter and binary black dwarfs will merge together creating new black holes, and these black holes will be consumed by even larger black holes. It might be that in the far future, all matter will exist in a few, truly massive black holes."

Note the "it might be." And again, this does not support your statement that "all matter and energy eventually leaves the universe the same way as it entered, through a singularity or singularities (as in black holes)." The mass-energy recycled through Hawking radiation does not "leave the universe." For that matter, nothing "entered" the universe "through" the big-bang singularity.

Tanelorn and Chalnoth, let's try to raise the level of discussion here. I've given you guys a reference to an actual scientific paper. You've given me statements that you think other people think X is true, and to a popular-level article that doesn't support your claim.

I turned up a good review article on this topic: Adams and Laughlin, A Dying Universe: The Long Term Fate and Evolution of Astrophysical Objects, , Rev.Mod.Phys.69:337-372,1997, http://arxiv.org/abs/astro-ph/9701131

"Thus, unless the dark matter particles themselves
decay into radiation, it seems that enough non-baryonic dark matter should survive to keep the universe
matter dominated at all future epochs; in addition, the leftover electrons and positrons will help prevent
the universe from becoming radiation dominated" (p. 38)

Ben, I have no proof, it was just one of several possible endings that I read in the popular press, possibly even before Hawking radiation was proposed, and to me at least, the one that seems the most elegant. ie. Matter and energy entered the universe via a singularity, and at the end leaves the universe via a singularity. As I said I am probably well out of date, but I will read the paper you linked soon. Just started reading it, it is impressive.

Would you not agree however that the orbit of all the stars in our galaxy over an extremely long time will eventually decay until the central black hole makes its kill?

Thanks Ben, I read that entirely. It seems that matter and energy never leaves the universe at all then. Perhaps it always was here then before the BB.

He does also mention that Cosmology is a fast moving science at the moment. In my design / integration phase in work we say that a product is still no where near ready to ship whilst it still rapidly undergoing mods due to bugs. If we consider how many cosmological theories have been proposed since the ancients first thought the earth was the center of the universe, then what is the chance that the latest theories are correct? However, I agree that the latest is probably the best we have.

Sorry, but I'm not buying it based on your secondhand impression that other people think it's inevitable.

The way I understand it, the argument goes that in order to have baryogensis, you need baryon number to not be exactly conserved. And if baryon number isn't exactly conserved, protons will, at some point, decay.

Yes, but the dark matter is expected to have been produced in equal parts matter and anti-matter, meaning it will eventually annihilate.

This would contradict the statement by Adams and Laughlin that I quoted in #15. Even if dark matter is an equal mix of particles and antiparticles (which I doubt can be stated with any certainty right now), there is the fact that some individual particles find themselves isolated inside their own cosmological horizons. This is discussed in both the Penrose paper and the Baez page.